Fixing Yamaha PSR-18 synthesizer keyboard
This Yamaha PSR-18 is an old (almost as old as me) entry level digital synthesiser that I owned for quite some time. Unfortunately due to continual use some of the keys started having issues, they needed to be pressed harder than others to make a sound. Of course this meant that the keyboard was hardly playable.
Under plastic keys of Yamaha PSR-18 it uses rubber membrane with conductive pads not unlike those found in TV remotes. When conductive pad presses against a printed contact it completes the circuit so it works as a switch. First I tried just to clean both surfaces. This did not help. It seems that with much use the conductive pad gets worn down. You can get brand new rubber membrane, but when I last looked they cost around 15$ per octave. At that price I could probably buy several entry level keyboards for the price of just replacing all the membranes.
** A few paragraphs on what not to do… Well you can try, but it didn’t work for me.
I tried several methods I thought could work. I first tried applying a few different brands of conductive glue I could get. Some were almost non-conductive when dry, but all of them hardened to a solid mass which either didn’t make the key work any better than before or simply crumbled away. The next thing to try was a conductive silver paint which adhered much better and in contrary to previous products was actually pretty conductive. This also didn’t produce the wanted improvement. You can see the silver conductive paint on the upper membrane in picture above.
Next I tried rubbing the pads with HB pencil to coat them with graphite. While this improved the situation quite a bit it still wasn’t perfect. Also this method really makes a mess in and on the contacts and rubber pads, so I really advice against it. I almost gave up on the keyboard at that point. Also there really didn’t seem to be any need for it as we bought a much better Yamaha P35 electric piano a few years ago.
** And now how I got it fixed 🙂
A few months ago I found this rubber key repair kit. It consists of some kind of silicon adhesive and replacement conductive rubber pads. I remembered the “archived” Yamaha PSR-18 and ordered the repair kit to give it a go.
The first step to fixing was to disassemble the keyboard. Of course I couldn’t just repair it without any peeking into where the music is made.
The PSR-18 seems to use the all-in-one synthesizer chip YM7137 and a YM7133 reverb chip which is on a piggyback PCB along with some DRAM.
Just for fun (and not to loose to much time if it didn’t work) I tried pushing the small conductive pad across printed contacts on the keyboard with pincers. It worked like a charm and all the notes sounded when they should 🙂
The instructions of the repair kit tell you to cut off a mm or so of the original pad, but there was enough space in the rubber membrane to situate the new conductive pads without any cutting needed.
I first cleaned each of the rubber pads from any junk. Here are a few pads partly through the cleaning sesion…
Then I glued on a new conductive pad. This is where you realize that there are quite a few keys on your keyboard, even if it is not a full size one 😉 And a few keys with brand new conductive pads already in place:
I did have to open the keyboard once more as after a week or so two of the keys stopped working. I seem to have introduced a few textile fibers when assembling the keyboard back. When the fibres got between the conductive pad and it’s contact on PCB they made the key less responsive to a press. After cleaning the debree out and being more careful at reassembly all the keys worked again.
It’s about a month from the repair and even after some extensive beating all the keys still work, so I call it a success 🙂
If getting a repair kit is not an option you can still get replacement conductive pads by cutting them from a sacraficial rubber keyboard, like from an TV remote. Just remember that you will need quite a bit of conductive pads for fully refurbishing a keyboard 😉 Also I wouldn’t try to replace conductive pads in keyboards with velocity / pressure sensing as that will probably not work.